1. Field of the Invention
This invention relates to a hybrid drive unit provided with a plurality of prime movers as a power source for driving a vehicle, and more particularly, to a control system for a hybrid drive unit, wherein an assist prime mover is connected through a transmission to an output member, to which a torque is transmitted from a main prime mover.
The present invention relates to the subject matter contained in Japanese Patent Application No.2003-171253, filed on Jun. 16, 2003, which is expressly incorporated herein by reference.
2. Description of Related Art
In a vehicular hybrid drive unit, an internal combustion engine such as a gasoline engine or a Diesel engine and an electric device such as a motor generator are generally used as prime movers. The modes of combination of those internal combustion engine and electric device are various, and the number of electric devices to be used is not limited to one but may be plural. In JP-A-2002-225578, for example, there is described the hybrid drive unit, in which an engine and a first motor generator are connected to each other through a synthesizing/distributing mechanism composed of a single pinion type planetary gear mechanism so that a torque is transmitted from the synthesizing/distributing mechanism to an output member, and in which a second motor generator is connected to the output member through a gear shift mechanism so that the output torque of the second motor generator is added as the so-called “assist torque” to the output member. Moreover, the gear shift mechanism is constructed of a planetary gear mechanism capable of being interchanged between a directly connected state and a decelerating state. In the directly connected state, the torque of the second motor generator is applied as it is to the output member. In the decelerating state, on the other hand, the torque of the second motor generator is raised and applied to the output member.
In the aforementioned hybrid drive unit, the second motor generator is controlled into a power mode or a regenerative mode so that a positive torque or a negative torque can be applied to the output member. Moreover, a deceleration state can be set by the transmission so that the second motor generator can be changed into a low torque type or a small size type.
In Japanese Published Examined Application 47-31773, moreover, there is disclosed a hybrid drive unit having a high brake and a low brake for interchanging between a high gear stage and a low gear stage. In case of switching to the high gear stage, the low brake is released and the high brake is applied. In case of switching to the low gear stage, on the other hand, the high brake is released and the low brake is applied. Thus, the interchange between the high gear stage and the low gear stage can be achieved by switching a connection of the brakes.
A gear shift in the transmission having such a construction as described in the aforementioned JP-A-2002-225578 is achieved by a control to change a ratio of speed between a member of an input side such as the motor generator and a member of an output side such as the output shaft. Consequently, the speeds of the transmission and the rotary member connected thereto are changed before and after the gear shift. An abrupt change in the speed makes an inertia torque accompanying the change in the speed larger so that so-called “shift shocks” is deteriorated. For this reason, in an ordinary automatic transmission for a vehicle according to the prior art, a torque capacity, i.e., an apply pressure of a frictional engagement device to participate in the shifting operation such as a clutch is controlled to change an output shaft torque smoothly.
However, if a timing of applying/releasing the clutch or the brake to participate in the shifting operation is off, a load added to the second motor generator fluctuates abruptly and thereby the speed of the second motor generator becomes too high or too low. Therefore, it takes time to raise the speed to a synchronous speed or lower, and energy to be absorbed in conjunction with the adjustment to the synchronous speed has to be increased. This may cause a delay in the gear shift and deterioration of durability of the frictional engagement device. Moreover, shocks accompanying the change in the speed may occur if the frictional engagement device is applied/released abruptly so as to avoid the delay in the gear shift.